Map
<p>
Colour the map with four colours, so that no two adjacent regions
have the same colour. (Regions touching at only one corner do not
count as adjacent.) There is a unique colouring consistent with the
coloured regions you are already given.
<p>
Drag from a coloured region to a blank one to colour the latter the
same colour as the former. Drag from outside the grid into a region
to erase its colour. (You cannot change the colours of the regions
you are given at the start of the game.)
<p>
Right-drag from a coloured region to a blank one to add dots marking
the latter region as <em>possibly</em> the same colour as the
former, or to remove those dots again.
